Oscillator circuits are used in many applications to generate signals having a desired frequency. For example, oscillator circuits are commonly used to generate clock signals which may for example be used for sampling other signals, like communication signals. Conventional oscillator circuits include for example ring oscillators or oscillators comprising an LC circuit portion comprising an inductivity (L) and a capacitance (C), which may be adjustable, and a so-called negative resistance circuit portion to compensate for energy losses of the LC circuit portion.
In many applications, adjustable oscillator circuits like digitally controlled oscillators (DCOs) where a frequency of an output signal can be adjusted by means of a digital control word or voltage controlled oscillators (VCO) where a frequency of an output signal can be adjusted by applying an appropriate voltage are used. Said oscillator circuits are often used in a so-called phase-locked loop (PLL), which regulates the output frequency of the oscillator signal depending on a reference signal.
The noise performance of such phase-locked loops is at least in part determined and sometimes even dominated by a phase noise of the oscillator circuit used. For many applications, for example communication applications requiring clock frequencies in the GHz range, low phase noise is important. On the other hand, in particular for mobile applications power consumption is an issue.